1. Field of the Invention
This invention relates to a torch ignition type internal combustion engine, and more particularly to a torch ignition type internal combustion engine which has no intake valve in the auxiliary combustion chamber.
2. Description of Prior Art
It is well known in the art to burn a rather lean air-fuel mixture in the engine cylinder in order to reduce the toxic components such as carbon monoxide, hydrocarbons and nitrogen oxides which are usually present in the exhaust gas of an engine. A lean air-fuel mixture, however, has potentially inferior ignitability and inferior flame propagation velocity, compared with a rich air-fuel mixture. Therefore, it is of crucial importance for an engine which burns a lean air-fuel mixture to stabilize the ignitability and increase its flame propagation velocity, otherwise a poor thermal efficiency and/or toxic exhaust gas (such as unburnt hydrocarbons) would result.
In order to overcome the aforementioned difficulty, there has been introduced the so-called torch ignition type internal combustion engine which has a main combustion chamber with an intake valve and an exhaust valve, and an auxiliary combustion chamber with an auxiliary intake valve, the engine being adapted to supply a lean air-fuel mixture to the main combustion chamber and a relatively rich mixture to the auxiliary combustion chamber through the respective intake valves. In such an engine system, the relatively rich air-fuel mixture in the auxiliary combustion chamber is first ignited and burned, the flames bursting from the auxiliary combustion chamber subsequently igniting the lean air-fuel mixture in the main combustion chamber. This internal combustion engine with an intake valve in the auxiliary combustion chamber is able to improve the ignitability of the lean air-fuel mixture and also to achieve high flame propagation velocity. On the other hand, such internal combustion engine invariably has complicated construction due to the requirement for the provision of the auxiliary intake valve in the auxiliary combustion chamber. Such a valve requires a complicated valve operating mechanism for operating the valves synchrounously with the engine revolution.
The present inventors have previously proposed a torch ignition type internal combustion engine which comprises a main combustion chamber with an intake valve and an exhaust valve, an auxiliary combustion chamber with no auxiliary intake valve, a passage interconnecting the main and auxiliary combustion chambers, and an ignition plug having its sparking electrodes located in the vicinity of the interconnecting passage. In this torch ignition type internal combustion engine, a lean air-fuel mixture sucked into the main combustion chamber through the intake valve during the intake stroke of the piston is pushed into the auxiliary combustion chamber during the succeeding compression stroke through the passage interconnecting the main and auxiliary combustion chambers. In this engine, a lean-fuel mixture can be ignited easily since there is only fresh air-fuel mixture around the sparking electrodes of the ignition plug which is located near the passage, that is, there is no residual gas remainining around the electrodes at the time of ignition, because the residual gas in the passage has been flown into the auxiliary combustion chamber by the lean mixture passing the passage during compression stroke. Then the lean air-fuel mixture in the main combustion chamber is ignited by the torch flames bursting not from the auxiliary combustion chamber, resulting from the mixture combustion in the auxiliary combustion chamber.
In the above-described torch ignition type internal combustion engine with no intake valve in the auxiliary cpombustion chamber, it is essential to control the mass and velocity of the torch flame coming out through the interconnecting passage to ensure optimum ignition and combustion of the lean air-fuel mixture in the main combustion chamber.